Thorium dilution effects of the heavy electron compound URu2Si2

We have investigated Th dilution effects for URu2Si2 by performing magnetic susceptibility chi and specific heat C measurements in a rich U-concentration range. We have observed that sharp and clear anomalies seen in chi and C of the pure URu2Si2 at T-0 = 17.5 K become weak and unclear by substituting only five percent of U with Th. At the same time, the magnitude of the c-axis susceptibility chi(c) and C/T at low temperature is enhanced, indicating that the gap formation in the density of states for heavy quasi-particles is sensitively suppressed. For 10% of Th substitution, on the other hand, we have found a new kink anomaly to appear in chi(c) at similar to 13.7 K, where C also shows a hump. This suggests the presence of antiferromagnetic instability in URu2Si2. (C) 2002 Elsevier Science B.V. All rights reserved.